A firm employs 100 workers at a vvage rate of $10 per hour, and 50 units of capital at a rate of $20 per hour. The marginal product of labour is 2, and the marginal product of capital is 4. The firm A. could reduce the cost of producing its current output level by employing more labour and less capital. B. is producing its current output level at the minimum cost. C. could increase its output at no extra cost by employing more capital and less labour. D. could reduce the cost of producing its current output level by employing more capital and less labour